APPLICATION NOTE

Looking into Batteries with
RISE Microscopy

Understanding structure-compositionproperty-performance relationships isfundamental in developing betterbatteries. RISE microscopy is anextremely useful technology forinvestigating these features.

APPLICATION NOTEThe Raman principle

No need for compromises

The Raman effect is based on theinelastic scattering of light by themolecules of gaseous, liquid or solidmaterials. The interaction of a moleculewith photons causes vibrations of its
chemical bonds, leading to specificenergy shifts in the scattered light. Thus,
any given chemical compound produces
a particular Raman spectrum when
excited and can be easily identified bythis individual “fingerprint.”

The Raman effect is extremely
weak, so every Raman photon isimportant for imaging. Therefore
WITec Raman imaging systems
combine an exceptionally sensitive
confocal microscope with an ultra-highthroughput spectrometer (UHTS).
Precise adjustment of all optical andmechanical elements guarantees
the highest resolution, outstanding
speed and extraordinary sensitivity –simultaneously!

Raman spectroscopy is a wellestablished, label-free and nondestructive method for analyzing themolecular composition of a sample.

Raman imaging
In Raman imaging, a confocal
microscope is combined with aspectrometer and a Raman spectrum
is recorded at every image pixel. The
resulting Raman image visualizes thedistribution of the sample’s compounds.
Due to the high confocality of WITec
Raman systems, volume scans and 3D
images can also be generated.

This optimization allows the detectionof Raman signals of even weak Raman
scatterers and extremely low material
concentrations or volumes with thelowest excitation energy levels. This isan unrivaled advantage of WITec
systems.

Resolution
Lateral resolution is
physically limited to~200 nm, dependingon the wavelength of
the incident light.

Speed
The more sensitive a system is, theshorter the acquisition time for a single
spectrum. WITec’s Ultrafast Raman
Imaging reduces acquisition times for
single Raman spectra down to well
below 1 ms.

Sensitivity
A high confocality increases the signal-to-noise ratio by
reducing the background. With the UHTS Series, WITecdeveloped lens-based, wavelength-optimized spectrometerswith a spectral resolution down to 0.1 cm-1 relativewavenumbers.

WITec Wissenschaftliche Instrumente und Technologie GmbH
Lise-Meitner-Str. 6, D-89081 Ulm, Germany
Tel. +49 (0) 731 140 700, Fax +49 (0) 731 140 70200
info@WITec.de, www.raman.oxinst.com

Raman Imaging on Lithium Ion BatteriesEver since Alessandro Volta invented
the voltaic pile, the first electric battery,research on generating electricity fromchemical reactions has continued
and led to the development of manyenergy storage designs, culminating inlithium-ion batteries (LIBs). Significant
improvements to LIBs resulted from theintroduction of new cathode materials
and the replacement of liquid electrolytes
by solid materials.

Non-destructive
Raman
imaging
microscopy can visualize structuraland chemical information acquired
from the battery’s internal components
such as their molecular composition,
grain fractures, the formation of solid
electrolyte interphase (SEI) layers anddegradation processes at the electrodes.

In the following, we document changes of
new and used electrodes with correlative
Raman imaging and scanning electron(RISE) microscopy.

Anodes usually consist of graphite andamorphous carbon. Cathode materials
used in commercial LIBs include
LiCoO2 (LCO), LiMn2O4 (LMO), LiNi0.84
Co0.12Al0.04O2 (NCA), LiNixCo1-x-yMnyO2(NCM/NMC), and LiFePO4 (LFP). Cobaltfree batteries such as spinel-structured
LiNi0.5Mn1.5O4 (LNMO) cells recently
became a focus of research as they avoid
requiring this expensive element.

RISE™ - Correlative Raman Imaging and Scanning Electron Microscopy
The combination of SEM, energy dispersive X-ray spectroscopy (EDX) andRaman imaging is an ideal correlative
approachformanyapplications.
Scanning electron microscopy (SEM)
uses the interaction of electrons with
the investigated material to reveal
the highest lateral resolution imagesof a specimen structure. The same
focused electron beam can be used togenerate energy dispersive X-ray spectra(EDX) for obtaining information on thechemical elements of the matter. This
technique, though very powerful, cannot
extract details of the bonding of atoms,
which would disclose the nature of themolecules in a sample. This task canbe achieved by fusing SEM with nondestructive Raman imaging.
This powerful combination is realized in
one instrument for Raman Imaging andScanning Electron (RISE) microscopy.
Due to an intelligent positioning system
the instrument enables diffraction limited
confocal Raman imaging from exactly
the same sample area as the SEM image.
Figure 1: Principle of RISE microscopy.
Samples are automatically transferred from one measuring position to the other within thevacuum chamber of the combined Raman-SEM instrument, streamlining the workflow anddrastically ​improving ease of use.

APPLICATION NOTE

Raman-EDS analysis of charged type 18650 Li-ion batteries
High-resolution
scanningelectronmicroscopy(SEM)enables
thedetailed analysis of the electrodes’
ultrastructure and energy-dispersive
X-ray spectroscopy (EDS) detects mostof their incorporated elements. Lithium
itself evades EDS detection because
it is too light. However, Li-containing
molecules are identifiable by their Raman
spectra, which can reveal changes intheir localization and concentration.
Raman spectroscopic imaging can also
differentiate polymorphic variations ofmolecules such as amorphous carbon
and graphite, which EDS is not able to do.

ABAll high-resolution Raman measurements
were performed using a WITec alpha300
confocal Raman microscope integrated
with an SEM system to enable the quickand easy correlation of ultrastructural

DIntensity [a.u.]Crelative wavenumbers [cm-1]

Figure 2: Raman microscopy and SEM-EDX mapping investigation of 18650 cell LMObatteries.
(A) SEM-EDX image of a cross section of a new battery. The cathode consists of Co/Ni-richregions (pink) and Mn-rich parts (cyan). The separator and the anode cannot be differentiated(black). Lithium is not detectable by EDX. (B) The area indicated by an inset in (A) was analyzed
by Raman microscopy. The resulting Raman image was overlaid on a white-light image. The
anode consists of graphitic (cyan) and amorphous carbon (blue), the separator is made up ofpolypropylene (yellow) and polyethylene sheets (green), and the cathode is comprised of LMO(red) and amorphous carbon (blue). (C) Raman spectra of the battery’s components. Colors asin (B). (D) Raman images of the separator before (above) and after (below) cycling. The process
induced changes in structure of the polypropylene sheets.
Sample courtesy of Timo Sörgel and Gerhard Schneider, Aalen University of Applied Sciences,Germany..

and chemical properties of the sample. An
alpha300 microscope can also operate
as a stand-alone, remotely controlled
instrument that provides the opportunity
to carry out the entire process ofdelicate sample preparation and Raman
imaging within the controlled gaseousenvironment of a glove box.
We examined two type 18650 Li-ion
batteries, one in its initial condition, while
the other cell had been cycled over
480 times, resulting in state of health ofapproximately 64%. Cross sections wereprepared under an argon atmosphere in aglove box. The SEM-EDS measurement of
the new battery reveals that the cathodeconsists of Co/Ni (pink) and Mn-rich parts(cyan) (Figure 2A). The separator and theanode are not visible, as the two polymers
as well as the two carbon molecules
cannot be distinguished from each other.
Also, lithium cannot be detected.
However, Raman imaging can visualize
graphite (cyan) and amorphous carbon(blue) in the anode and amorphous carbon
and lithium with manganese oxides (red)in the cathode (Figure 2B). The separator
is built up from a layer of polyethylene(PE) (green) between two layers of poly
propylene (PP) (yellow). All of themolecules mentioned were identified bytheir Raman spectra (Figure 2C). During
cycling the separators‘ polymers undergomolecular deterioration (Figure 2D). While
the outer layers of the separator of thenew battery include only uniaxial PP, thepolymer chains change their directions
during cycling, appearing as bi-axial PP
in the used battery. It has been describedthat changes in the composition of
separators influence significantly theperfor­mance of a Li-ion battery.

WITec Wissenschaftliche Instrumente und Technologie GmbH
Lise-Meitner-Str. 6, D-89081 Ulm, Germany
Tel. +49 (0) 731 140 700, Fax +49 (0) 731 140 70200
info@WITec.de, www.raman.oxinst.com

Impact of fast charging cycles on Li-NMC batteries

In the RISE image of the new, charged
cathode (Figure 3A) its particles appear
to consist of uniform lithium nickel cobalt
manganese oxide. The components
were identified by their typical spectral
peaks around 580 (Li-NMC, blue), 1300
cm-1 and 1550 cm-1 (amorphous carbon,red) wavenumbers (Figure 3C).
Rapidcycling
inducedsignificant
changes in lithiation of the particles
as indicated by changes in the Raman
spectra (green) (Figure 3B). Raman peaks
have broadened and shifted (Figure 3D).
The Raman data reveals local variations
even at the single particle level.
In Figure 3B one particle is characterizedby two spectra, one of which corresponds
to the Li-NMC spectrum of the nativeelectrode, indicating that this particle
might not have participated in the cycling
process. Lorentzian fitting of the spectral
peak positions of another particle also
shows a high level of inhomogeneityand degradation in the form of cracks(Figure 3E). More significant cracking wasdetected near the separation membrane(not shown).

BC

D

Intensity [a.u.]

Local deterioration of microstructure in
NMC battery electrodes subjected tofast charging and long-term cycling wasstudied using a Raman system integrated
with a Tescan SEM that includes a
focused ion beam (FIB). Cross sections
were created with the FIB for imaging.

A

Intensity [a.u.]

We performed analyses of NMC batteries
that underwent fast recharging. Rapidcharging of empty batteries is in great
demand in the automotive sector, yet it
impairs the batteries’ performance. The
investigated NMC cell was subjected
to 400 cycles, leading to a 40% lossof capacity. Changes in performanceare often a result of inhomogeneous
degradation in battery electrodes.

relative wavenumbers [cm-1

relative wavenumbers [cm-1]

E
Figure 3: RISE analysis of the cathode of afast-cycled Li-NMC battery.
(A) Cross section of an uncycled cathode.
Particles embedded in amorphous carbon(red) contain uniformly-distributed lithium
nickel cobalt manganese oxide (blue). (B)Cross section of a cycled and rapidly chargedcathode. Compared to the uncycled cathodethe particles appear inhomogeneous. Oneparticle (bottom left) shows a completely
different composition, including a spectrum(blue) identical to the Li-NMC spectrum of
the uncycled electrode. (C) Typical Raman
spectra of Li-NMC (blue) and amorphous
carbon (red) of the uncycled cathode. (D)Raman spectra of molecules detected in thecycled cathode. Changes in peak positions
and peak width indicate variance of Li-NMC
composition. (E) RISE image of a particle ofa cycled cathode that reveals changes in LiNMC composition and substantial structuraldegradation.
Sample courtesy of Dean Miller (Tescan USA)

WITec Microscopesalpha300 S:
Scanning Near-field
Optical Microscopealpha300 A:
Atomic ForceMicroscopealpha300 R:
Confocal Raman
Microscopealpha300 apyron™: AutomatedConfocal Raman Microscope

Find your regional WITec and Oxford Instruments
contact at https://raman.oxinst.com/contact
WITec Headquarters
WITec Wissenschaftliche Instrumente und Technologie GmbH
Lise-Meitner-Str. 6, D-89081 Ulm, Germany
Phone +49 (0) 731 140 700, Fax +49 (0) 731 14070 200
info@witec.de, https://raman.oxinst.com

alpha300 Ri:
Inverted Confocal
Raman Microscopealpha300 access:Confocal Micro-Raman System

RISE®: Raman Imaging
and Scanning ElectronMicroscope